RFC: The GNU C Library is no longer *the* C library on most systems with the Linux kernel (and hasn't been for a while).

[Alfred M. Szmidt]

   AFAIK, a "GNU system" is Hurd?  So just tweaking it a bit and
   avoiding machine classification seems best suited.

There are several GNU systems, GNU/Hurd is one, and another one is
GNU/Linux, then you have GNU/kFreeBSD as well.